Targeted Disruption of Aldh1a1 (Raldh1) Provides Evidence for a Complex Mechanism of Retinoic Acid Synthesis in the Developing Retina

Abstract

Genetic studies have shown that retinoic acid (RA) signaling is required for mouse retina development, controlled in part by an RA-generating aldehyde dehydrogenase encoded by Aldh1a2 (Raldh2) expressed transiently in the optic vesicles. We examined the function of a related gene, Aldh1a1 (Raldh1), expressed throughout development in the dorsal retina. Raldh1 ؊/؊ mice are viable and exhibit apparently normal retinal morphology despite a complete absence of Raldh1 protein in the dorsal neural retina. RA signaling in the optic cup, detected by using a RARE-lacZ transgene, is not significantly altered in Raldh1 ؊/؊ embryos at embryonic day 10.5, possibly due to normal expression of Aldh1a3 (Raldh3) in dorsal retinal pigment epithelium and ventral neural retina. However, at E16.5 when Raldh3 is expressed ventrally but not dorsally, Raldh1 embryos lack RARE-lacZ expression in the dorsal retina and its retinocollicular axonal projections, whereas normal RARE-lacZ expression is detected in the ventral retina and its axonal projections. Retrograde labeling of adult Raldh1؊/؊ retinal ganglion cells indicated that dorsal retinal axons project to the superior colliculus, and electroretinography revealed no defect of adult visual function, suggesting that dorsal RA signaling is unnecessary for retinal ganglion cell axonal outgrowth. We observed that RA synthesis in liver of Raldh1 ؊/؊ mice was greatly reduced, thus showing that Raldh1 indeed participates in RA synthesis in vivo. Our findings suggest that RA signaling may be necessary only during early stages of retina development and that if RA synthesis is needed in dorsal retina, it is catalyzed by multiple enzymes, including Raldh1.

Retinoic acid down‐regulates Tbx1 expression in vivo and in vitro

“…The explanation for this discrepancy between the mouse and avian data may be that, in the VAD embryos, there is no dietary vitamin A. Thus, all the embryonic RA production pathways, including those mediated by retinol dehydrogenases, e.g., adh1 and adh4 (Rossant et al, 1991;Vonesch et al, 1994;Haselbeck and Duester, 1998), and retinaldehyde dehydrogenases such as Raldh1, 2 and 3 (Blentic et al, 2003;Fan et al, 2003) are blocked. In the hypomorphic raldh2 mouse mutants, only one RA-producing enzymatic pathway is partially blocked, perhaps resulting in a less severe effect upon Tbx1 expression.…”

Transcriptional Regulation of Cannabinoid Receptor-1 Expression in the Liver by Retinoic Acid Acting via Retinoic Acid Receptor-γ

“…This resistance has been attributed to the elevated tissue levels of retinaldehyde and its ability to inhibit adipogenesis by suppressing peroxisome proliferation-activated receptor ␥ and RXR␣ responses. Raldh1 knock-out mice are largely deficient in RA in the liver (14), and it is possible that at the greatly reduced hepatic RA levels, the high fat diet may have failed to induce CB 1 R expression in tissues involved in metabolic control, and the resulting reduction in endocannabinoid "tone" may have contributed to the lean phenotype of these animals. Further experiments are under way to test this possibility.…”

“…Mice with hepatocyte-specific knock-out of CB 1 R (LCB 1 Ϫ/Ϫ mice) were generated as described (1). Raldh1 Ϫ/Ϫ mice on a mixed 129/C57Bl/6 background were generated as described (14). All experiments with knock-out mice used the corresponding homozygous wild-type (ϩ/ϩ) littermates as controls.…”

Fate of retinoic acid–activated embryonic cell lineages

“…The rationale for these studies is that most, if not all, tissues express at least one of the RARs (Dolle, 2009 for a review), that should activate the reporter upon binding of endogenous RA. The RARE-hsp68-lacZ transgene has been widely used in subsequent studies (e.g., Malpel et al, 2000;Mic et al, 2002;Niederreither et al, 2002b;Fan et al, 2003;Matt et al, 2003Matt et al, , 2005Yashiro et al, 2004;Sirbu et al, 2005;Molotkov et al, 2006;Sirbu and Duester, 2006;Ribes et al, 2009;Zhao et al, 2009). Three lines of evidence have validated this transgene as a reliable indicator of RA activity: (1) there is a close match between the patterns of lacZ activity and the expression patterns of RA-synthesizing enzymes (Rdh10, Raldhs) at early embryonic stages, (2) activity of the lacZ reporter is severely down-regulated in knockout mice for the above enzymes (Niederreither et al, 1999;Mic et al, 2002;Matt et al, 2005;Molotkov et al, 2006;Sandell et al, 2007), (3) on the other hand, the reporter is almost ubiquitously activated within 6 h after administration of a bolus dose of RA to the pregnant mothers (Rossant et al, 1991), and is ectopically activated when RA-metabolizing enzymes are absent Sakai et al, 2001;Uehara et al, 2009).…”